1. Field of the Invention
The invention relates to a dispensing device. In particular, it relates to a dispensing device capable of determining a trace mount of a sample, i.e., sucking or dispensing the sample, which comprises a flexible tube provided with a pipetting nozzle at an end thereof, a washing solution supplier supplying a washing solution to the flexible tube and the pipetting nozzle, a syringe connected to another end of the flexible tube and a control section for controlling the driving of the washing solution supplier and the syringe.
2. Description of the Related Art
A conventional dispensing device is mainly composed of a tube provided with a pipetting nozzle at an end and a syringe connected to another end of the tube, which enables a sample or a washing solution to be sucked or discharged through a pipetting nozzle by actuating a piston in the syringe.
Some dispensing devices comprising a washing solution supplier for washing the pipetting nozzle, tube and syringe through which the sample passes wash the pipetting nozzle by supplying a pressed washing solution from the syringe side to the pipetting nozzle via the flexible tube or from the pipetting nozzle to the syringe via the flexible tube.
In addition, the following prior arts are known. Japanese Laid-open Patent Publication No. Hei 4 (1992)-274764 discloses a structure wherein the pressure in a tube is detected by a sensor when moving a pipetting nozzle to a predetermined place after finishing suction for measurement and the pressure in the tube is maintained at a certain level by actuating the syringe for suction to prevent a sample liquid from dropping out from the tip of the pipetting nozzle.
Japanese Laid-open Patent Publication No. Hei 6 (1994)-27121 describes a syringe works for suction that cuts the liquid drop on the tip of the nozzle after discharging the liquid. Further, Japanese Laid-open Patent Publication No. Hei 6 (1994)-34497 describes a syringe that comprises a pipe provided with a suction valve and an ejecting valve, and a syringe works for suction that cuts off the liquid drop on the tip of the nozzle after discharging the liquid.
The conventional dispensing device may be used for an automatic analyzer such as an automated immunochemical analyzer, in which the pipetting nozzle is inserted in a sample container and the syringe starts sucking a predetermined mount of the sample through the flexible tube. Then, the pipetting nozzle is transmitted to a reaction container. When the pipetting nozzle is inserted in the reaction container, the syringe starts discharging the predetermined amount of the sample sucked in the flexible tube or syringe.
Subsequently, the pipetting nozzle is washed by the washing solution supplier. In this process, the washing solution or air for washing the pipetting nozzle was strongly discharged from the syringe side to the tip of the pipetting nozzle or, on the contrary, strongly sucked from the tip of the pipetting nozzle to the syringe side, thereby cleanly washing contamination inside of the pipetting nozzle caused by sample pipetting. Then, the pipetting nozzle is transmitted between the sample container and the reaction container relatively to enter another sucking/dispensing process.
The dispensing device disclosed in Japanese Laid-open Patent Publication No. Hei 4 (1992)-274764 has defects in the delay of response and the easy generation of uneven sensitivity because feedback control is conducted based on the pressure data in the tube detected by the sensor. It is hard to determine at a high speed and with good accuracy.
According to the dispensing devices disclosed in Japanese Laid-open Patent Publication Nos. Hei 6 (1994)-27121 and Hei 6 (1994)-34497, the liquid drop on the tip of the pipetting nozzle can be cut off. However, these devices do not solve the problems of the delay of determination time and of the deterioration of accuracy owing to the expansion and contraction of the tube connected to the nozzle and syringe.
When the washing solution is supplied from the syringe side of the dispensing device in the washing process, pressure is applied to the inside of the tube and the tube is expanded (see FIG. 6), whereby the inner volume of the flexible tube 3 is increased. The expanded tube 3 regains the initial shape for several seconds after washing. The gradual restoration of the expanded tube leads the washing solution which remains in the tube 3 to the tip of the pipetting nozzle 2 as the liquid drop (the liquid drop shown in FIG. 8).
When the washing solution is sucked from the tip of the pipetting nozzle 2 in the washing process, the tube 3 is contracted (see FIG. 7). The contracted tube 3 gradually regains the initial shape by its own restoration force. However, the pressure inside of the tube 3 is reduced because of the restoration, so that the washing solution is sucked into the pipetting nozzle 2.
The tube 3 deformed in the washing process induces determination errors of the sample, which causes a significant problem in determining a trace amount of sample such as a several micron liters.
Generally, the mount of the water solution used in the washing process ranges from several times to several thousand times the amount of the liquid sample. It may take 10 seconds or more for the expanded or contracted tube deformed by discharging or sucking such a great amount of washing solution to regain its initial shape and allow another pipetting action of a trace amount of the sample. The time causes a delay in the measurement.
On the other hand, if the flexible tube described above is not used, it would be difficult to move the pipetting nozzle between a plurality of reaction containers up and down or rotationally (relative transmittance).